1. FIELD OF THE INVENTION
This invention relates generally to indwelling catheters, and more particularly to systems for keeping the proximal orifices of such catheters free of clogging deposits, large suspended particles, and contaminating bacteria. Such catheters are used in medical procedures for both humans and animals.
(An "indwelling" catheter is one that is emplaced and left in place for protracted periods, such as fifteen minutes or longer. It has been known to leave catheters in place for more than two years. In this document the word "proximal" is used with respect to the patient's body, not with respect to the instrumentation at the other end of the catheter. The word "medical" is used to encompass surgical as well as medicinal therapies. The word "bacteria" is used to encompass bacteria, viruses, fungi, and other bioactive materials.)
2. PRIOR ART
Indwelling catheters are well known, both for supplying medication and nutriments--as, for instance, in intravenous tubes--and for draining urine, exudates or other fluids from a patient's body. A major problem in the protracted use of such catheters arises from clogging or contamination of their channels and proximal orifices, and from large particles suspended in the fluids.
This problem is more crucial in drains, since the conditions that give rise to the drainage requirement in the first place are generally the same conditions that produce undesirable substances such as congealing mucus, pus, and sometimes even particulate organic debris.
Of course clogging of an indwelling drain is a serious matter since the drainage required by the patient's condition is thereby defeated. These undesirable substances, however, not only mechanically obstruct the orifices but also carry bacteria, which often lodge in stagnant regions at the orifices. Such an accumulation of bacteria is a breeding site for disease germs that may not even be active in the patient to begin with, and thus creates a serious risk of secondary infection and severe complications.
Supply tubes such as intravenous catheters are also subject to contamination by bacteria already within the patient's body or introduced by external contamination, and to a lesser extent are subject to clogging. Supply catheters that carry nutriments are an attractive site for accumulation of bacteria that divert the nutriment supply. In this way a dual negative effect is generated: the nutriment needed by the patient is at least partially withdrawn, and the patient's condition may be threatened by the bioaction of the bacteria.
In the case of catheters that deliver medication, bacteria threaten the integrity of the medical bioactivity in totally unpredictable ways. Bacteria can impair or completely metabolize the medicine or can even amplify its action--as by stripping away moderating molecular groups or excipients.
Regular cleaning is accordingly an essential part of any therapy that requires indwelling catheterization. Unfortunately, however, the usual procedure for cleaning a catheter entails removal from the patient. Sometimes such a catheter is replaced by a clean unit and taken away for cleaning elsewhere, and sometimes it is forthwith cleaned and put back into the patient's body.
In either case, the likelihood of trauma to the patient is substantial. The opportunity for aggravation of the foregoing problems by inadequate cleaning is likewise substantial.
Patients are known to develop several kinds of undesirable reactions to repeated removal and replacement of catheters. Repetitive insertion of intravenous tubes, for example, badly irritates and scars the areas where the needles are emplaced--sometimes so seriously that the intravenous supply must be moved to an entirely different part of the body. Patient morale correspondingly suffers, often enough to cause significant depression and psychosomatically induced deterioration of the patient's physical condition. Furthermore, each removal and replacement increases the chance of bacterial contamination and blood clots, which clog or can add to the infection, or both.
When incompletely cleaned catheters are placed in a patient's body, the result can be disastrous. Infection that may have been localized in the area of the proximal orifices of the catheter can spread throughout the entire route of the catheter passage. When an incompletely cleaned catheter taken from one patient is emplaced in a different patient, the spread of local infection and even fatal disease assumes catastrophic character.
Although the present state of the art in catheter cleaning is not really effective at all against bacterial accumulations, it should be understood that even far more effective techniques would be hard put to completely eliminate bacterial attack. The reason is that bacteria actually have a mechanism for surviving (as a group) cleaning techniques. In particular, bacteria mutate rapidly and thereby avoid the effects of almost any adverse condition that can be pragmatically imposed upon them. Thus some bacteria are found alive and well in permafrost, while others survive temperatures over 3000.degree. F. and some have been found doing nicely in lava flows. Some of these bacteria metabolize sulfur compounds; hence it may be appreciated that mere chemical agents--at least those that are in the least compatible with the survival of the patient--are hopelessly inadequate over any protracted treatment period.
All of these conditions are aggravated by mechanical stress, not only at the surface of the patient's body but at every point where the catheter is subject to flexure during emplacement or during the patient's necessary daily activities.
Foregoing references to incomplete cleaning of indwelling catheters, tragically enough, are far from academic. It is well documented, though ironic, that in this era of advanced scientific sophistication the most basic sanitation procedures are more honored in the breach than in the observance, at many major medical facilities.
Based upon a recent public-health survey it has been asserted that a significant percentage of all hospitalized patients contract an infection while in the hospital. The percentage is even higher (reportedly much higher) in such vital areas as intensive-care units. Whether due to economics, faulty management or societal degradation--all of which causes have been invoked in the commentary--this phenomenon poses a monumental threat to the effectiveness of institutional therapies.
Earlier efforts to avoid the customary steps of manual withdrawal, cleaning and reemplacement have been ineffectual, impractical or at least too cumbersome to gain general acceptance.
The state of the art for in situ cleaning, with respect to actual widespread usage in medical facilities, is simply irrigation of the catheter with any of a great variety of supposedly cleansing solutions. Such irrigation is not done by machinery but simply by hand, using a syringe. Typical of this approach is U.S. Pat. No. 4,296,747 to Ogle, describing an improved device for introducing cleansing or irrigating fluid into a Foley catheter--a catheter assembly that is used to drain urine from the bladder.
Irrigation techniques, while generally practical, are not adequately effective. Other systems tend toward the converse: for example, U.S. Pat. No. 3,416,532 to Grossman discloses a self-scraping drainage catheter formed of inner and outer tubes. The outer tube defines numerous orifices near its proximal end, and the inner tube has a slanted sharp edge near its proximal end. When the orifices become clogged, the inner tube may be reciprocated so that the slanted edge tends to scrape off clots or other clogging of the perforations in the outer tube.
Though elaborate and awkward to use, this system is probably helpful in removing debris that extends through the perforations into the space within the outer tube. Such a system, however, does little to clean away accumulated substances that are actually within the orifices themselves and do not extend into the inner tube, or accumulations that are just outside the catheter in the patient's body.
Other patents which teach systems for unclogging catheter perforations include U.S. Pat. Nos. 3,863,641 to Popa, 2,642,873 to Rice, 4,228,802 to Trott, 3,601,128 to Hakim, and 3,955,574 to Rubinstein.
Popa describes a dual-catheter thoracic aspiration drain used especially after heart surgery or after a traumatism in the thorax. In this device an inner catheter ends in a balloon that can be inflated to seal against the internal surface of the outer catheter. While thus sealed the balloon is drawn outwardly, creating a suction that forcibly pulls debris into the inner tube, whence it is more readily drawn out by the aspirator. This system plainly relies upon well-trained personnel for vigilant monitoring and manipulation.
Rice's invention is similar to Grossman's, but in Rice the inner tube has orifices aligned with those in the outer tube, and is rotated rather than reciprocated. Trott's proposed catheter likewise would have a "detachable auger assembly" and a "mechanical expanding device" for breaking up clots and debris at the proximal entrance to the catheter, and also includes an annular lumen for introduction of irrigating fluid.
Hakim describes a "ventriculoatrial shunt"--a device for draining cerebrospinal fluid into the venous blood system to relieve hydrocephalus. In this system, clogging of the cerebroventricular catheter by the choroid plexus or by other matter is discouraged by a sort of backflushing technique. A portion of the cerebrospinal fluid is valved to cyclically flow back into the cerebral ventricle. This technique is highly specialized to situations in which the primary danger is of clogging by material of a fibrous character, and also appears sufficiently fussy as to require knowledgeable and virtually constant monitoring. Such an approach is undoubtedly justified in critical circumstances such as brain trauma, but would be difficult or impractical to sustain in less acute cases.
Rubinstein too discloses a cyclical alternation of vacuum and pressure applied to a catheter drain, so that suction is periodically interrupted by predetermined periods of blowing, to help keep the proximal entrances clear.
As stated earlier, all these known systems either are impractical for general use or are simply ineffective for protracted catheterization.
In another area, it is known to use vibration for clearing obstructions from certain internal passageways and cavities of a patient's body. U.S. Pat No. 3,352,303 to Delaney reveals an ultrasonic vibratory system for "lysis of blood clots" in veins and arteries. U.S. Pat. No. 3,433,226 to Boyd describes a similar system for "decimation of atheromatous plaques"--i.e., of fatty degenerations of the arterial lining.
U.S. Pat. No. 3,861,391 to Antonevich and Goodfriend provides for ultrasonic "disintegration of urinary calculi." This theme is elaborated by U.S. Pat. Nos. 3,927,675 to Pohlman and 4,192,294 to Vasilevsky et al.; and expanded by Tessler in U.S. Pat. No. 4,030,1505 to encompass disintegration of kidney and bladder stones.
Some Russian workers have reported efforts to destroy bacteria using ultrasonic vibrations. These efforts, however, have not been directed to cleansing of catheters or even to channeling of such vibrations into sites within a patient's body. Furthermore they have not addressed the difficult mutational-escape problem discussed above.
The prior art thus deals to some extent with ultrasound as a means for removal of preexisting deposits such as blood clots, arterial plaque, and urinary-tract stones through working catheters briefly inserted for the purpose. It does not, however, teach or even suggest that ultrasound could be used to maintain free flow and sanitation of a catheter itself, or in particular of an indwelling catheter.
Of less interest are ultrasonic catheter devices for determining the location of objects within a patient's body. For example Colley, in U.S. Pat. Nos. 4,354,500 through 4,354,502, proposes to find air emboli using such devices; and Kubota, in U.S. Pat. Nos. 4,344,436 and 4,346,702, describes how to use such devices to find the location of a catheter tip relative to the patient's body.